As a method for producing 2-cyclohexene-1-ol by hydrogenolysis of cyclohexenyl hydroperoxide, Japanese Patent Publication No. 2536/1966 reports a hydrogenolysis method using metallic palladium and a compound of lead or bismuth as a catalyst, which is carried out in the presence of a liquid hydrocarbon solvent, a hydrophilic solvent of lower alcohols and an organic base at about room temperature. As described below, however, the catalyst does not exhibit high activity by itself, and the activity of the catalyst is only 84% at maximum though improvement in the activity is attempted by adding a hydrophilic solvent and an organic base.
Incidentally, in Example 1 of the above reference, it is described that 2-cyclohexene-1-ol is obtained at a yield of 84% by hydrogenolysis of cyclohexenyl hydroperoxide with a metallic palladium/lead acetate catalyst using cyclohexene as a liquid hydrocarbon, ethanol as a hydrophilic solvent and quinoline as an organic base. On the other hand, Example 1-2 of the reference exemplifies the same reaction as Example 1 except that the organic base is not employed. The yield of 2-cyclohexene-1-ol is 63%.
In Example 5 of this patent publication, the reaction for obtaining 2-cyclohexene-1-ol is carried out by changing the amount of ethanol. As a result, too much reduction in the amount of ethanol causes the aggregation of the catalyst and deteriorates its activity. These disclosures show that it is essential to combine the hydrophilic solvent such as alcohol with the organic base in this method.
Further, the specification of this Japanese patent publication discloses that ethylenic hydrocarbon such as cyclohexene is inactive in a reduction reaction by hydrogen when used as a solvent. In the above Examples, however, the hydrogenation ratio of cyclohexene as a solvent is not disclosed.
Bull. Soc. Chim. France, 1964(6), P1302 contains an article of the inventors of Japanese Patent Publication No. 2536/1966.
Although the content of this article is almost the same as that of the Japanese patent publication, it further discloses that the hydrogenation ratio of cyclohexene is less than 1% when cyclohexene is employed as a solvent. However, a specific value of the hydrogenation ratio is not indicated.
Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk 1958, P133 exemplifies a method for hydrogenolysis of cyclohexenyl hydroperoxide in an ethanol solvent using Raney nickel, platinum black and palladium black as a catalyst. However, the resultant product is only cyclohexanol having hydrogenated double bonds.
All the conventional methods have been carried out in the presence of a hydrophilic solvent such as alcohol, and preferable ones have been all carried out in the presence of a hydrophilic solvent and an organic base. Particularly, the methods wherein 2-cyclohexene-1-ol is obtained at a relatively high yield have been all carried out in the presence of an organic base such as quinoline using a catalyst comprising metallic palladium and lead or bismuth. However, the presence of plural components in the reaction system makes the separation of the product unduly complicated. Especially when 1,3-cyclohexadiene is produced by the dehydration reaction of the resultant 2-cyclohexene-1-ol using an acid catalyst, a special treatment such as rinsing is required since the acid catalyst is poisoned if the organic base remains even in a very small amount. Therefore, the use of organic bases is not industrially preferable.